Boston and surrounding towns are in a state of lockdown while heavily armed police hunt for the surviving marathon bombing suspect who escaped after a car chase and shootout in the early hours of Friday.

The man, identified as Dzhokhar Tsarnaev, 19, remains on the loose, more than 16 hours after he and his brother Tamerlan, 26, killed a campus police officer at the Massachusetts Institute of Technology, sparking a chain of events that continued through Friday. The men had been identified earlier on Thursday as the main suspects in the bombing that left three dead and more than 170 injured.

In what law enforcement officials described as an ambush-style attack, Sean Collier, 26, was shot multiple times at about 10.30pm as he sat in his police cruiser within the MIT campus.

Tamerlan Tsarnaev died after an ensuing car chase that ended with a shootout in the suburb of Watertown, but his younger brother managed to break through the line of officers and escape. An officer with the Massachusetts Bay Transportation Authority was wounded.

Hundreds of officers are now amassed in Watertown, supported by bomb squad robotic equipment and armored vehicles, giving the quiet town the appearance of a war zone. Across the greater Boston area, almost a million people remain confined to their homes, mass transit systems are suspended and a no-fly zone has been imposed as the hunt for the fugitive continued. Boston Bruins and Red Sox games scheduled for Friday night have been cancelled.

Swat teams, carrying military-style rifles and protective shields, are proceeding house to house in Watertown. State police said that a controlled explosion would take place on Friday afternoon at an address on Norfolk Street, which was surrounded by police snipers earlier in the day.

National Guard helicopters have also landed at the campus of the University of Massachusetts Dartmouth, where Dzhokhar Tsarnaev was a student. The campus was evacuated on Friday.

The brothers were said by officials to have Chechen heritage. The family moved to Cambridge in 2003 from Kyrgyzstan, where Tamerlan Tsarnaev was born, according to an uncle. Dzhokhar Tsarnaev, who was born in the Dagestan region, became a naturalised US citizen last year.

Their father, Anzor Tsarnaev, speaking to the Associated Press from the Russian city of Makhachkala, described his younger son as "a true angel", who was studying medicine. "He is such an intelligent boy. We expected him to come on holidays here," the father said.

The apparent Chechen connection prompted immediate speculation that the bomb attack was motivated by the Islamist separatist movement there, but no link has been established so far.

Tamerlan Tsarnaev spent six months in Russia last year, travelling from New York to Moscow in January 2012 and returning to the US in July. His father, who insisted his sons were innocent and had been framed, told the New York Times that he had stayed with him in Makhachkala, the capital of Dagestan, but they had also gone together to Chechnya to visit relatives.

Their uncle, Ruslan Tsarni, who lives in Montgomery Village, Maryland, described the brothers as "losers" who had brought shame on all Chechens. Speaking on live television outside him home, he urged his nephew: "Dzhokhar, if you are alive, turn yourself in and ask for forgiveness."

Maret Tsarnaeva, an aunt of the brothers, said that Tamerlan Tsarnaev seemed not yet to have found "himself yet in America, and recently went from being a devout Muslim who prays no more than once per day to one who prayed five times a day.

He had married and had a three-year-old daughter in the US, she told reporters in Toronto.

"He has a wife in Boston from a Christian family, so you can't tie it to religion," she said. "At that age all they want is love, so he found his love, he married, he had a daughter, and he was very happy about his daughter."

She described the boys as "normal young men" who are "athletic" and "smart." Their father, she said, doted on the boys. "Anzor is a very loving and soft-hearted father."

Dzokhar appears to have been a good student, having received a $2,500 scholarship from the city of Cambridge in 2011 to pursue college. He was also named a wrestling all-star at his high school the same year.

According to Dzhokhar Tsarnaev's own account on the Russian social networking site VKontakte, he attended School No 1 in Makhachkala, the capital of Dagestan, from 1999 to 2001, graduating from the Cambridge Rindge and Latin School, a Massachusetts high school, two years ago.

On his VKontakte page, Tsarnaev says he considers "career and money" most important in life. As his worldview, he wrote: "Islam".

The page says Tsarnaev speaks English, Russian and Chechen, and belongs to a number of groups devoted to Chechnya. Dagestan, a republic neighbouring Chechnya, maintains a small Chechen minority.

A local TV station in Maryland interviewed another uncle, Alvi Tsarni. He told the reporter that he had heard about his nephews' involvement this morning from a sister-in-law. "She was crying and she said that Tamerlan was killed.

In imperfect English, Tsarni, who said he had lived in the United States for 10 years, said he had not spoken with the brothers for a long time because of "problems family." Then "yesterday he called me," Tsarni said – he appeared to be referring to Tamerlan – "and said 'Forgive me, and we will talk to this now. From now we will be together ever."

The uncle said that if his nephews were confirmed as the marathon bombers he would personally kneel in front of the families of the victims of the blasts and beg forgiveness.

The dramatic events began around 10.20pm on Thursday night with the armed robbery at the 7-Eleven store in Cambridge Central Square. About 10 minutes later, the men killed the MIT police officer Sean Collier, then hijacked a black Mercedes SUV, holding the driver captive at gunpoint for the next 30 minutes before they released him uninjured.

The car then sped in the direction of Watertown, prompting a huge police chase with local, state and federal law enforcers in pursuit. Towards the end of the chase, the suspects threw explosive devices out of the car. One bomb, described by eyewitnesses as resembling a pressure cooker, exploded in mid-air, causing a fireball and injuring many police officers.

Seconds later, Tamerlan Tsarnaev ran towards police, where he was either tackled or shot, lying prone on the ground before he was taken captive and rushed to hospital, where he died at about 1.35am. His younger brother escaped, driving a car straight through the police line, heading west. The car was abandoned a little further down the street, and the younger Tsarnaev made off on foot.

"There is a massive manhunt under way, [and] a lot of law enforcement involved in that," Massachusetts governor Deval Patrick told reporters on Friday morning. "We've got every asset that we can possibly muster on the ground right now."